1. Field of the Invention
The present invention relates to a light source device having a life detection device for detecting the end of useful life of a light source such as Xenon tube used in a photographic enlarger or the like.
2. Description of the Prior Art
A light sources device for use in an enlarger having one or more light source such as Xenon tubes is well known. In the above type of the light source, the Xenon tubes are sequentially driven to emit light in a controlled manner so that a desired light value is emitted. The above type of the light source is disclosed in the U.S. Pat. No. 4,551,011 in which the device is used in an enlarger the number of light emission and each emitted light amount is determined such that the exposure time is approximately the same regardless of the total amount of exposure. In the light source mentioned above, if one of the Xenon tubes fails in emitting light due to end of its useful life of the Xenon tube, there will occur a discontinuation of light from the light source, whereby the exposure of the enlarger is incomplete and a good photographic print can not be obtained.
Conventional light source devices, however, can not detect such failure of light emission of the Xenon tube. In the case where the light source device with the inoperative tube installed is repeatedly used, not only the quality of the photographic print is deteriorated due to discontinuation of light but also a Xenon tube drive circuit would be damaged.